Method of pickling and pickling compositions



Patented Oct. 19, 1954 UNITED STATES PATET OFFICE METHOD OF PICKLIN GAND EICKLING COMPOSITIONS tion of Delaware No Drawing. ApplicationOctober 18, 1951, Serial No. 251,981

14 Claims.

This invention relates to the acid pickling of metals, more particularlythe acid pickling of steel, and to new and useful pickling compositions.

One of the objects of the invention is to provide a new and improvedmethod of pickling ferrous metals in which the pickling process isgreatly accelerated.

Another object of the invention is to provide a method of pickling steelsheets prior to galvanizing.

Still another object of the invention is to provide a method of picklingwhich results in a longer life for the pickle tank or vessel where thepickling operation is practiced.

Another object of the invention is to provide a pickling method whichcan operate satisfactorily at relatively high iron concentrations.

Still a further object of the invention is to provide a method ofpickling ferrous metals to produce surface characteristics that bringabout better adherence of other metals which are electrodeposited onsaid ferrous metals.

A further object of the invention is to provide new and useful picklingcompositions which can be added to acid pickling baths in order toproduce new and improved results. Other objects will appear hereinafter.

These objects are accomplished in accordance with this invention byproviding a pickling bath containing a compound capable of liberatingcolloidal sulfur, preferably sodium thiosulfate, and a chromiumaldonate, e. g., a reaction product of a water soluble chromic compoundof an alkali metal with an aldonic acid in proportions such that theratio of chromium atom to alkali metal atom is within the range of 1:1to 1:3, the ratio of chromium atom to the aldonic acid molecule iswithin the range of 1:1 to 1:3, and the ratio of total alkali metal atomplus the aldonic acid molecule to chromium atom is at least 3:1.

The chromium aldonates preferably employed for the purpose of theinvention are the chromium gluconates, but it will be understood thatthe chromium aldonates may be derived from other aldonic acids, as, forexample, mannonic, arabonic, galactonic and xylonic. These acids areobtainedv by the oxidation of the corresponding aldoses and all of them,including gluconic acid, have alpha and beta lactone forms. The alkalimetal ion may be either sodium, potassium or lithium. Chromium aldonateswhich are satisfactory for the purpose of the present invention aredescribed in U. S. Patent No. 2,428,- 356.

The invention will be illustrated but is not limited by the followingexamples.

Example I A composition suitable for use as an addition agent to an acidpickling bath was prepared by mixing together the following ingredients:

2703 pounds of water 2'70 pounds 5 ounces dextrose 27 pounds /2 ouncecaustic soda 1900 pounds sodium thiosulfate 3720 cc. chromium gluconate,derived by mixing together:

48 pounds of sodium hydroxide 48 pounds of chromic anhydride 444 poundsof 50% gluconic acid, and making up to gallons of water as described inExample I of U. S. Patent No. 2,428,356.

The aforementioned ingredients were mixed in the order given. Causticsoda and dextrose are optional ingredients, the dextrose being added asa reducing agent and the caustic soda to make it possible to ship theproduct in steel drums.

Example II A hydrochloric acid pickling bath was prepared containing 10to 15% I-ICl. The composition described in Example I was added inproportions of 0.5 to 2.0 gallons per thousand gallons of the picklingbath at the start of the pickling operation. In the bath cold rolledcarbon steel sheets were pickled. To replace the dragout of acid anadditional 0.5 to 2 gallons of the composition of Example I were addedper thousand pounds loss of HCl as the pickling process continued.

In comparative tests using 2 parts of the addition agent described inExample I per thousand parts of 15% H0; solution, compared with a 15%I-ICl solution containing no addition agent, it was found that the bathcontaining the addition agent produced uniform attack on the steel in 3minutes, which could not be accomplished in 20 minutes without theaddition agent.

Example III solution may be varied plus or minus 50% of the quantitygiven in Example I.

The employment of a substance such as sodium thiosulfate which liberatescolloidal sulfur in the pickling solution is not claimed herein per sebut is the subject of another application of one of the joint inventors,United States Serial No. 694,424, filed August 31, 1946. Itwill beunderstood that other substances capable of liberating colloidal sulfuras, for example, sodium polysulfide may be employed in the practice ofthe invention.

The chromium aldonate apparently acts as a cathode depolarizer of thecouples formed on the surface of the metal which is being pickled. As aresult, the pickling action is exceedingly rapid and at the same time auniform attack of the acid on the metal is obtained.

The thiosulfate tends to prevent the formation of alpha and gamma ironoxide and the sulfur which is liberated to some extent also acts as adepolarizing agent. The resultant pickling bath therefore may bedescribed as a depolarized pickle bath. The quantity of sodiumthiosulfate or chemically equivalent amount of another sulfur liberatingcompound is subject to variation but is preferably within the range of lto 8 parts of sodium thiosulfate per 700 parts of 7% sulfuric acid orabout 1 to 8 parts colloidal reactive sulfur in 5000 parts of sulfuricacid.

With the pickling composition described in Example I the optimum resultsare obtained by using 1 to 3 parts of said composition per thousandparts by weight of a pickling solution containing either sulfuric acidor hydrochloric acid in the concentrations previously described.

The pickling temperatures are preferably within the range of 120 F. to200 F. in sulfuric acid pickling baths and within the range of 60 F. to120 F. in hydrochloric acid pickling baths.

In the practice of this invention results have been produced which havenot before been attained in the acid pickling of ferrous metals.

In the practice of this invention results have been produced which havenot before been attained in the acid pickling of ferrous metals.

The invention is especially useful in pickling sheet steel which is tobe galvanized. The pickling action provided by the invention appears toproduce better wetting between the surface of the sheet and the metalwhich is applied in the galvanizing process. One of the principaladvantages of the invention is the provision of a more uniform pinpointetch with an acceleration of pickling speeds. The practice of theinvention is particularly desirable in that it provides longer life ofthe pickle tank. It also has the advantage that the process may beoperated with the same solution for a longer period of time because theoperation proceeds satisfactorily at relatively high ironconcentrations. The ferrous metals which are pickled in acid picklingbaths in accordance with the practice of the invention have excellentsurface characteristics and provide better adherence forelectrodeposited metals than ferrous metals which have been acid pickledby ordinary methods.

The invention is hereby claimed as follows:

1. A process of conditioning ferrous metal surfaces which comprisesimmersing the ferrous metal surface to be conditioned in an acidpickling bath containing a chromium aldonate and a compound capable ofliberating elemental colloidal sulfur, the quantity of said last namedcompound being effective to liberate colloidal sulfur in a sufficientlysmall amount to remain dispersed in colloidal form.

2. A process of conditioning ferrous metal surfaces which comprisesimmersing the ferrous metal surface to be conditioned in a sulfuric acidpicking bath containing a chromium aldonate and a compound capable ofliberating elemental colloidal sulfur, the quantity of said last namedcompound being effective to liberate colloidal sulfur in a sufficientlysmall amount to remain dispersed in colloidal form.

3. A process of conditioning ferrous metal surfaces which comprisesimmersing the ferrous metal surface to be conditioned in a hydrochloricacid pickling bath containing a chromium aldonate and a compound capableof liberating elemental colloidal sulfur, the quantity of said lastnamed compound being effective to liberate colloidal sulfur in asufficiently small amount to remain dispersed in colloidal form.

4. A process of conditioning ferrous metal surfaces which comprisesimmersing the ferrous metal surface to be conditioned in an acidpickling bath containing a chromium gluconate and a compound capable ofliberating elemental colloidal sulfur, the quantity of said last namedcompound being enective to liberate colloidal sulfur in a sufficientlysmall amount to remain dispersed in colloidal form.

5. A process of conditioning ferrous metal surfaces which comprisesimmersing the ferrous metal surface to be conditioned in a sulfuric acidpickling bath containing a chromium gluconate and a compound capable ofliberating elemental colloidal sulfur, the quantity of said last namedcompound being effective to liberate colloidal sulfur in a sufiicientlysmall amount to remain dis persed in colloidal form.

6. A process of conditioning ferrous metal surfaces which comprisesimmersing the ferrous metal surface to be conditioned in a hydrochloricacid pickling bath containing a chromium gluconate and a compoundcapable of liberating elemental colloidal sulfur, the quantity of saidlast named compound being efiective to liberate colloidal sulfur in asufficiently small amount to remain dispersed in colloidal form.

7. A process of conditioning ferrous metal surfaces which comprisesimmersing the ferrous metal surface to be conditioned in an acidpickling bath containing chromium gluconate and sodium thiosulfate, thequantity of sodium thiosulfate being sufficient to liberate 1 to 8 partsof colloidal sulfur to 5000 parts of the acid contained in said bath.

8. An acid pickling bath containing a chromium aldonate and a compoundcapable of liberating elemental colloidal sulfur, the quantity of saidlast named compound being effective to liberate about 1 to 8 partscolloidal sulfur to 5000 parts of the acid content in said bath.

9. A sulfuric acid pickling bath containing a chromium aldonate and acompound capable of liberating elemental colloidal sulfur, the quantityof said last named compound being effective to liberate about 1 to 8parts colloidal sulfur to 5000 parts of the acid content in said bath.

10. A hydrochloric acid pickling bath containing a chromium aldonate anda compound capable of liberating elemental colloidal sulfur, thequantity of said last named compound being effective to liberate about 1to 8 parts colloidal sulfur to 5000 parts of the acid content in said.bath.

11. An acid pickling bath containing a chromium gluconate and a.compound capable of libcrating elemental colloidal sulfur, the quantityof said last named compound being efiective to liberate about 1 to 8parts colloidal sulfur to 5000 parts of the acid content in said bath.

12. A sulfuric acid pickling bath containing a chromium gluconate and acompound capable of liberating elemental colloidal sulfur, the quantityof said last named compound being effective to liberate about 1 to 8parts colloidal sulfur to 5000 parts of the acid content in said bath.

13. A hydrochloric acid pickling bath containing a chromium gluconateand a compound capable of liberating elemental colloidal sulfur, thequantity of said last named compound being effective to liberate about 1to 8 parts colloidal sull5 fur to 5000 parts of the acid content in saidbath.

14. An acid pickling bath containing chromium gluconate and sodiumthiosulfate, the quantity of sodium thiosulfate being sufficient toliberate 1 to 8 parts of colloidal sulfur to 5000 parts of 5 the acidcontained in said bath.

References Cited in the file of this patent UNITED STATES PATENTS 10Number Name Date 1,995,766 Chester Mar. 26, 1935 2,249,383 Hilty July15, 1941 2,428,356 Chester et a1. Oct. 7, 1947 OTHER REFERENCES ModernInorganic Chemistry, Mellor, pub. Longmans Green, p. 475.

1. A PROCESS OF CONDITIONING FERROUS METAL SURFACES WHICH COMPRISESIMMERSING THE FERROUS METAL SURFACE TO BE CONDITIONED IN AN ACIDPICKLING BATH CONTAINING A CHROMIUM ALDONATE AND A COMPOUND CAPABLE OFLIBERATING ELEMENTAL COLLOIDAL SULFUR, THE QUANTITY OF SAID LAST NAMEDCOMPOUND BEING EFFECTIVE TO LIBERATE COLLOIDAL SULFUR IN A SUFFICIENTLYSMALL AMOUNT TO REMAIN DISPERSED IN COLLOIDAL FORM.